Fine- to medium-grained, dark gray to black intrusive igneous rock. Diabase is one of the dark rocks known commercially as “black granite.” It is extremely hard and tough and is commonly quarried for crushed stone, under the name “trap.” Chemically and mineralogically, diabase closely resembles the volcanic rock basalt, but it is generally somewhat coarser grained.

Learn more about diabase with a free trial on Britannica.com.